As one of the defeated candidates for the Commons Speakership remarked during today's hustings, public expectations of what the winner can achieve are "getting more unrealistic by the day".

But it was also common ground among all 10 contestants that voters expect some changes after the expenses scandal. Enthusiastic or not, they know they must deliver.

But what can the Speaker John Bercow do? Part of the impotence of the legislature, which the candidates also bemoaned, stems from "modern­isation" reforms started under John Major that centralised power within the executive.

They were happily endorsed by Tony Blair's shadow team, which could see benefits for an ambitious new government that was keen not to be pinned down by backbench MPs.

Thus reforms continued under Blair, sometimes in the name of shorter, "family-friendly" hours which kept MPs busy in daylight hours and scattered them to their John Lewis-furnished flats at night, their scope for independent action "streamlined" and feather-bedded away. Old fashioned rebels, who knew the procedures backwards, retired or faded, along with prime ministerial involvement in debates.

Gordon Brown was present and silent today (both rare events) but he appeared to be doing paperwork. One test of Bercow's authority will be to curtail that sort of discourtesy, along with the 20-year habit of announcing policy to Radio 4's Today programme, not to MPs. Well within living memory the BBC was not allowed to discuss issues expected to be debated by MPs inside 14 days. There must be a better balance.

This will depend in part on the character of the Speaker, hence the candidates' stress on their record of defiance against their own party or government. It is not easy to grant an inconvenient emergency statement or debate, not easy to defy pressure and grant an awkward vote on the Iraq war.

Even powerful Speakers such as Betty Boothroyd can confirm that. Like all Speakers since Westminster's closed world opened to broadcasting in 1977, she had to be a public figure, media-savvy while aloof from controversy.

A Speaker has three roles: overseeing the complex management of Westminster and its staff; being its public face abroad (the domestic role must now grow); and controlling the Commons, MPs and ministers alike. The last now matters most. There is some evidence ex-ministers have the confidence and experience to throw their weight about. In a bitter contest in 1951 the new Tory government imposed William "Shakes" Morrison, who turned out to be excellent. Selwyn Lloyd, a feeble chancellor and pliable foreign secretary, was also much admired (1971-76). Labour's George Thomas deferred too much to Margaret Thatcher.

The weekend note by Commons clerk Robert Rogers sets out the Speaker's personal scope to create snappier, more accessible procedures and face down ministers. But it will need backbenchers, working together against their party whips, to recapture lost control over select committees and debate, just at a time when their confidence has been squashed by expenses abuses and public trust is low. Sustained reform under Speaker Bercow will need both luck and judgment.